(1) Technical Field
The present disclosure relates to an organic electroluminescence (EL) element emitting blue light (referred to as a blue organic EL element in the following), an organic EL display panel, and a manufacturing method of a blue organic EL element. In particular, the present disclosure relates to a technology improving the quality of an organic light-emitting layer formed by using a wet process.
(2) Description of Related Art
A typical organic EL element includes, layered in the stated order, a first electrode, an organic light-emitting layer, and a second electrode. Such a typical organic EL element emits light due to organic light-emitting material contained in the organic light-emitting layer being put in excitation state when carriers (i.e., holes and electrons) supplied from the first electrode and the second electrode recombine in the organic light-emitting layer. Meanwhile, a typical organic EL display panel includes a plurality of organic EL elements forming a matrix along a top surface of a substrate, and displays images by combining light emitted from the organic EL elements. Recently, development is in progress of a technology increasing both the performance and the mass-productivity of such organic EL elements and organic EL display panels.
As an example of such technology, conventional technology is disclosed of utilizing the effect of optical interference occurring between light reflected by the first electrode, light reflected by the second electrode, etc., in order to improve the color purity, the luminance, etc., of light emitted from organic EL elements and organic EL display panels (for example, refer to Japanese Patent Application Publication No. 2000-323277). Specifically, this conventional technology improves the color purity, the luminance, etc., of light emitted from an organic EL element by adjusting layer structure of the organic EL element (e.g., by adjusting the arrangement of layers and the thickness of layers) and thereby optimizing the difference between lengths of optical paths along which light travels in the organic EL element. In addition, conventional technology is disclosed of strengthening the effect of the optical interference by forming an optical microresonator in an organic EL element by providing both the first electrode and the second electrode with optical reflectivity, and thereby causing an optical stationary wave to be generated in the organic EL element (for example, refer to Japanese Patent Application Publication No. H11-288786).
Further, conventional technology is disclosed of forming organic light-emitting layers by using a so-called wet process, which involves application and drying of ink containing an organic light-emitting material dissolved in an organic solvent, in order to improve the accuracy with which organic light-emitting layers are formed and to improve the efficiency of material use during the forming of organic light-emitting layers (for example, refer to Japanese Patent Application Publication No. 2014-075260). Typically, when forming organic light-emitting layers by using a wet process, the organic light-emitting layers are formed within openings defined by a bank layer. Forming organic light-emitting layers within such openings has the effect of reducing a decrease in accuracy with which the organic light-emitting layers are formed that would otherwise occur due to an undesirable spread of applied ink.